Seasonal and Nocturnal Variations of the Mesospheric Sodium Layer at Starfire Optical Range, New Mexico

The seasonal variations of the mesospheric sodium layer structure over Starfire Optical Range (SOR: 35ºN, 106.5ºW), New Mexico are characterized using 46 night data of Na wind/temperature lidar observations collected from Jan. 1998 to May 2000. The column abundance has a mean value of 5.06 x 109 cm -2 and strong annual oscillations of with a maximum in November and a minimum in June and July. The annual mean rms width of the sodium layer is 4.30 km and the mean centroid height is 91.60 km. Semiannual oscillations are evident in seasonal variations of the rms width and the centroid height. Their mean nocturnal variations show effects of tides. The photo-ionization during daytime and recombination processes of Na at night, as well as tidal dynamics, induce strong nocturnal variations in the sodium abundance with a minimum just before midnight and a maximum just before sunrise